As shown in FIG. 9, in order to shorten the startup time for scanography, the stop position of a gantry rotating unit at the waiting time (the time of stoppage of rotation) of the gantry is set to locate an X-ray tube 101 at 0° (the uppermost portion). An X-ray tube cooling device 103 is mounted next to the X-ray tube 101. The X-ray tube cooling device 103 performs cooling by circulating oil between itself and the X-ray tube 101. The X-ray tube cooling device 103 is called oil cooler. A gantry side surface cover 105 is provided with an outlet 107 to efficiently exhaust heat conducted from the oil cooler 103 to the outside of the gantry. A cooling fan 109 is provided in a local portion of the main frame near the outlet 107. The cooling fan 109 sends air inside the gantry to the outlet 107 to exhaust the air outside. As shown in FIG. 9, since the X-ray tube 101 is placed at 0° at the waiting time of the gantry, the oil cooler 103 is placed at a position shifted from 0°.
As shown in FIG. 10, a lower cover 111 is provided with an inlet 113 for sucking air into the gantry. Air with lower temperature than air inside the gantry, is sucked into the gantry through the inlet 113. The sucked air mainly flows from the inlet 113 to the outlet 107. Since the X-ray tube 101 is placed at the nearly 0° position at the waiting time of the gantry, stagnation points of air occur in portions above an X-ray detector 115 and a DAS (data acquisition system) 117 arranged to face the X-ray tube 101 through the rotation axis. This makes it difficult to cool the X-ray detector 115 and the data acquisition system 117. There is room for improvement in cooling efficiency with respect to the X-ray detector 115 and the data acquisition system 117.
In addition, as shown in FIG. 10, another outlet 119 is provided to exhaust air in an area on the opposite side to the oil cooler 103 inside the gantry in the lateral direction to the outside of the gantry. A cooling fan 121 is also provided near the outlet 119. The cooling fan 121 exhausts air in the area on the opposite side to the oil cooler 103 to the outside of the gantry. However, since the main heat source inside the gantry is the oil cooler 103, there is room for improvement in exhaust efficiency based on the cooling fan 121 as compared with the cooling fan 109.